One of the disadvantages of compression ignition internal combustion engines, especially of the low compression ratio type described in U.S. Pat. No. 3,526,214 is the occasional production of "white smoke" which is unburned fuel vapor suspended in the exhaust gas. White smoke occurs particularly during cold starting, idling, and low load operation when the temperature distribution of the intake air supplied to the cylinder is uneven or insufficient to completely combust the fuel in the cylinder. Thus, white smoke is materially different from black smoke which is formed of carbon particles produced when the compression temperature is adequate to support combustion but the local oxygen supply is insufficient to oxidize all of the carbon in the fuel.
In order to reduce and eliminate the production of white smoke, numerous systems have been employed. One method involves heating the intake air of a compression ignition internal combustion engine to effect complete combustion. One system used for heating intake air includes a computer-controlled electric manifold heater system. In this system, heater elements are connected to respective heater relays which, in turn, are preferably connected to a thermistor through an electronic control module. This system is powered by the vehicle battery. The heater elements operate similarly to induction heating coils, and heat the air in the intake manifold selectively under certain engine temperature conditions to improve combustion. For example, U.S. Pat. No. 4,512,322 to Barcy discloses part of such a system: an electric air heater using heating coils disposed in the path of the intake air and powered by an electric power source.
Another device for controlling white smoke emission is a KSB (fuel pump cold start system) valve as manufactured by the Robert Bosch Co. for use on their fuel pumps and described in the 1989 Dodge Ram/Cummins Turbodiesel 5.9 Liter Student Reference Book. Like the manifold heater system described above, this valve is controlled by a module responding to a thermistor that senses intake manifold temperature. When the thermistor senses an intake manifold temperature of less than 15 degrees C, the control module keeps the KSB valve closed. The closed valve keeps fuel from returning to the low pressure side of the fuel supply pump, thus increasing pump housing pressure and forcing full advance of the fuel pump cam roller ring that controls fuel injection timing.
The electric manifold heater system and the KSB valve system can be used together advantageously since both systems can be controlled by the same thermistor and electronic control module. Significantly, both the electric manifold heater system and the Bosch KSB valve require testing after the system is installed in the vehicle. When white smoke output has been observed, testing is necessary as part of a troubleshooting operation to diagnose the cause of the apparent system failure. The systems also require periodic testing as part of a general maintenance or emissions inspection program.
In accomplishing this testing, it is not sufficient to merely turn on the engine and observe operation of the heater and KSB systems. The heater system is designed to operate in different modes depending on engine temperature; yet, the engine will likely not operate over the entire operating temperature range during the observation, and the operating temperature range cannot be controlled by the individual testing the heater system. Thus, the response of the system to the full range of operating conditions and engine temperatures encountered in the field cannot be determined by observing system operation in the shop.
Therefore, there is a need for a testing system which tests the operation of the components of an electric intake manifold heater system and which can simulate all of the operating temperature ranges sensed by the thermistor. Although individual systems exist for bench-testing the various components and circuitry of an electric manifold heating system, no testing system for post-installation and assembly testing has been developed.